Time for me to go put some 100 octane in baby!!!!
Originally Posted by Sal@Evolve
Here is the stock full throttle ignition target for an M3:
With high octane fuel these targets will be met.
With 91 US they simply will not.
Light knock is detected and the ECU is continually pushing and retarding ignition.
You can 'force' ignition by raising the preset ignition maps by quite a few degrees.